The present invention relates to methods and compositions for suppressing crystallization in brines during drilling operations, particularly at high pressures and low temperatures. Preferred brines are completion fluids, most preferably clear brines.
The petroleum industry continues to expand deepwater exploration and drilling efforts in many areas of the world. As drilling water depth increases, the potential for various problems also increases. One such problem is the crystallization of brines during drilling operations.
Clear brines commonly have been used in drilling operations since the 1970""s, and are advantageous for many reasons. One advantage is that clear brines tend to minimize damage at high pressures. Clear brines commonly are used as completion fluids, perforating fluids, packer fluids, and in pay zone drill-in fluids.
Early use of clear brines during drilling operations quickly revealed a significant drawbackxe2x80x94untimely crystallization of the salts in the brine, causing the salts to fall out of solution. The formation of crystallized solids in the work string can plug the workstring, causing expensive downtime and requiring that the plug be cleared. The crystalline solids also can conceal the presence of a gas bubble in the workstring below the crystallized solids. As the plugged lines are cleared, a concealed gas bubble can cause the well to blow out, resulting in loss of the entire rig.
Until recently, the pressure effect on crystallization has not presented a problemxe2x80x94even in exceptionally high pressure work. This is because the highest pressures typically have been encountered together with the highest temperatures, which reduces the risk of crystallization. However, a combination of high pressure and low temperature does occur in at least two cases: 1) when working in exceptionally deep waters where the hydrostatic pressure at the sea floor (mud-line) is combined with near freezing temperatures; and, 2) in colder climates, when conducting pressure tests of lines and similar equipment, such as blow-out preventers.
Previous methods used to cope with crystallization have not proven to be effective under all conditions. Brines are needed which effectively suppress crystallization under a wide variety of temperature and pressure conditions.
A brine comprising an aqueous solution comprising at least one salt at a density sufficient to crystallize out of the brine at a crystallization point comprising a given temperature and a given pressure, and a crystallization point suppressant consisting essentially of one or more low molecular weight water-soluble organic compounds other than methanol in an amount effective to suppress the crystallization point.